The present invention is directed generally to anti-glare devices and more particularly to a filter for a transmission screen or liquid crystal display (LCD) for eliminating glare caused by ambient light.
It has long been recognized that the front face of a transmission screen such as the cathode ray tube (CRT) of an ordinary television screen or the CRT of a computer terminal produces glare caused by ambient light. As a result of this phenomena, a substantial amount of glare is encountered when viewing, for example, a CRT in a brightly lit room. The glare problem can be reduced by increasing the intensity of the radiation from the CRT. However, manufacturing CRT's capable of producing the intensity necessary to overcome glare encountered in a brightly lit room greatly increases the cost of the CRT. It is therefore desirable to produce a filter or overlay which will reduce the glare produced by ambient light.
My U.S. patent application Ser. No. 716,237, filed Aug. 20, 1976, now abandoned, was directed to an overlay or filter for the viewing surface of a television screen to reduce front face glare. The overlay is comprised of a sheet of transparent material having a planar back face and a front face having a plurality of V-shaped grooves therein such that the overlay, when viewed from the side, has a sawtooth profile. The overlay is flexible such that a film of oil is applied to the back surface of the overlay and, by pressing the overlay against the viewing surface of the television screen, the overlay adheres thereto. The adherence of the overlay to the television screen together with the film of oil therebetween minimizes the optical interference between the overlay and the television screen. Unfortunately, this overlay did not produce satisfactory results. The overlay produced images, known as echo images, which interfered with the intelligence displayed on the television screen.
In my U.S. Pat. No. 4,165,920, a front face glare reduction overlay including an echo reduction improvement is disclosed. The U.S. Pat. No. 4,165,920, which was filed during the pendency of my abandoned U.S. patent application Ser. No. 716,237, is directed to an improvement in the overlay disclosed in such abandoned application. The improvement involves applying a coating of opaque material to the peaks of the sawtooth forming the front surface of the overlay. It is also disclosed in the U.S. Pat. No. 4,165,920 that the horizontal portion of the sawtooth should be inclined approximately six degrees from the horizontal and the vertical portion of the sawtooth should be inclined approximately thirty degrees from the vertical. Using these angles in conjunction with the opaque material provides a front face glare reduction overlay which produces satisfactory results. However, despite the satisfactory results, it proved difficult to manufacture the peaks of the sawtooth with a sharp point. Because the peaks tended to have a round or lenticular shape, they were difficult to coat with the opaque material. Light from the transmission screen was refracted by the uncoated or partially coated peaks in a number of different vertical directions, thereby creating a further problem with echo images.
In an effort to provide an overlay or filter for the viewing surface of a transmission screen to reduce front face glare which is both inexpensive and easy to manufacture, I developed an anti-glare device which is described and illustrated in U.S Pat. No. 4,473,277. The anti-glare device of the U.S. Pat. No. 4,473,277 need not be applied directly to the surface of the CRT but can, in fact, be positioned a discrete distance therefrom. With the back surface thus free of the requirement of being tightly fitted to the transmission screen, it was discovered that the opaque material applied to the peaks of the sawtooth could be eliminated if a circular polarizer or some similar filter means was mounted to the back surface of the anti-glare device. The anti-glare device disclosed in the U.S. Pat. No. 4,473,277 proved to be easy to manufacture and free of echo image problems. However, the cost of the circular polarizer together with the time and expense required by the bonding step which bonded the circular polarizer to the anti-glare device increased the cost of the device.